According to Bloomberg, the lobbyists' proposal suggests
changing "shall" to "may issue final regulations
implementing" the Volcker rule.

As it stands, Dodd's bill already includes a
weaker version of the Volcker Rule. The
original rule would ban banks from proprietary trading or
investing in hedge funds and private equity funds.

Dodd's Volcker rule would ban banks from prop trading at some
point in the future.

Now Dodd's committee is gathering to weigh watering the Volcker
rule down even more. They will consider a number of amendments,
one of which is whether or not to change the word "shall"
[implement in the future] to the word "may" [implement in the
future].

Bloomberg says the lobbyists for financial firms, who
proposed the change, are essentially suggesting that regulators
first "study the issue to see if it’s needed, then give
regulators the option of imposing a ban." (emphasis
ours).

"Shall" is just one word, but it's definitive. "May" implies that
it's followed by "or may not." So if just that one word is
changed to "may", it wouldn't be impossible for regulators to
decide to opt out of reform and allow all banks to continue prop
trading.